They’re called the "Underground Astronauts" - six women with a very specific set of qualifications who descended deep underground last month to retrieve the ancient remains of human ancestors.

To qualify for the mission, the women needed an advanced degree in paleontology, archaeology or a related field. They needed caving experience. And they needed to be able to fit through a very, very narrow cave opening - just 18 centimeters wide, or about seven inches.

University of Iowa paleoanthropology doctoral candidate K. Lindsay Eaves met those requirements, which is how she became part of the Rising Star expedition in South Africa.

The team brought up hundreds of fossils from a cavern in the Cradle of Humankind. The Cradle of Humankind is a World Heritage Site in South Africa that is home to around 40 percent of the world’s known hominin fossils. Hominin refers to both modern humans and their extinct ancestors.

Eaves said she isn’t allowed to talk about exactly what the scientists discovered beneath the ground until more analysis has been done and a scientific journal article is published. But she did say the finds - bones and fragments of skeletons, likely from well over a million years ago - were remarkable. She described listening to the scientists who were examining the fossils she and the other cavers were bringing to the surface.

“There were a lot of ‘Wows,’ and a few ‘I’ve never seen that before,’ and even some ‘What the hell?’” she said. “I think everyone’s going to be really just ecstatic. If I wasn’t a part of this it would still be one of the big moments in paleoanthropology.”

She’s not the only one to think the Rising Star discoveries were exceptional.

The excavation, a collaboration between the South African University of Witwatersrand and National Geographic, has garnered international media attention. National Geographic videographers followed the team throughout the excavation, and a documentary is in the works.

The fossil trove was first discovered by recreational cavers from South Africa’s Speleological Exploration Club, who brought the cave to the attention of National Geographic Explorer-in-Residence Lee Berger. Berger then organized the dig.

"We can confirm this site is the richest early hominin site in South Africa," he told the International Science Times. "The quality of preservation is unprecedented.”

The team uncovered over 1,000 fossils which could provide clues to human evolution.

“It’s important because it comes from a time when our earliest ancestors were still evolving their aptitude for bipedalism (walking on two feet), which is how we spot our ancestors in the fossil record,” Eaves said. “It’s sort of the adolescence of the human lineage. They’re not humans but getting pretty close.”

For Eaves, 28, who lives in Austin, Texas, this trip was just the beginning of the project. The scientists will head back to South Africa, probably early next year, to process what they’ve found. Eventually there will be more trips underground - the team has only started uncovering what the Rising Star caves offer, Eaves said.

In the meantime, she’s working to finish her PhD and is hoping to develop a website for children about the Rising Star expedition.

“So few of us can actually fit down into the cave,” she said. “We’re trying to make it as accessible to the rest of the world as possible.”